Health chiefs confirmed at the weekend that three children remain in hospital, all of whom were described as stable.

Meanwhile it has been reported that two families who visited the farm months before the first suspected outbreak suffered serious health problems.

The family of Holly Nethercote, who visited the farm in March, said they were told that her case was a one-off after she was admitted to hospital with kidney failure.

A spokesman for the HPA said they would not comment on individual cases but the families’ claims would be looked into by an ongoing investigation.

The spokesman added: “There are always sporadic cases of E.coli throughout the year. Sometimes the source is not clear, and all of that will be considered as part of the investigation.”

The chief executive of the HPA has promised to set up an external investigation into the outbreak, led by George Griffin, professor of infectious diseases and medicine at St George’s University of London.

A farm in North Yorkshire became the fifth to close on the advice of the Health Protection Agency (HPA) on Friday.

The Big Sheep and Little Cow farm in Bedale partially closed as a precautionary measure after three case of E.coli were linked to the farm, the HPA said.